There's a few hotels in the airport precinct - the Parkroyal, Ibis, Ibis Styles, Novotel, Holiday Inn. Most are within walking distance. Cheaper options if you are willing to travel a little from the airport but I wouldn't recommend it, you'd easily spend the difference (not to mention the time involved) on taxis.
Walkability wise my recommendations would be Parkroyal, Ibis Styles or Novotel. The former is right next to T2/3, the two latter are a short walk down from T4